There are basically two different series within the Ender saga: There is the Ender Series, and there is the Bean Series.
and Ender's Shadow
tell the same story from the perspective of two different characters (Ender and Bean). The movie is supposedly bridging these two books together.
is the first novel in the Ender series, though it is almost like The Hobbit in that its story is basically a prequel to a more tightly connected trilogy:
Speaker for the Dead
Children of the Mind
is the first book of the "Bean Series," which follows up with...
Shadow of the Hegemon
Shadow of the Giant
Now, if you're still reading the series after all of this...
Ender in Exile
is a more recent novel that takes place in between Ender's Game
and Speaker for the Dead
, but I would still recommend reading it after you've read all the other Ender books.
Shadows in Flight
is like an epilogue to the Bean saga. It is a story very disconnected from the main series of Bean books and takes place several years later, but I found it a very fitting ending to the series.
And NOW the most recent book in the series is called Earth Unaware
, which is a prequel to everything. I haven't started it yet, but it is sitting on my shelf. It is supposedly the story of the first Formic (Bugger) War.